The present invention relates to the use of ozone to increase the efficiency of the laundry wash process and, more particularly, to controlling the delivery of ozone to washing machines according to the current washer cycles of the machines.
Ozone (O.sub.3) is a triatomic allotrope of oxygen in which the ozone molecule consists of three oxygen atoms in contrast to the two oxygen atoms which comprise the typical oxygen molecule (O.sub.2). Ozone can be generated by passing air or oxygen through a high intensity electric field. Some of the oxygen molecules will be energized and will split into two separate atoms. These individual oxygen atoms will then form weak bonds with other oxygen molecules. The ozone molecule is oxygen in a highly reactive form. It has a tendency to give up its extra oxygen atom and gain electrons. This molecular structure gives ozone its high oxidizing power which allows ozone to react rapidly with a large variety of compounds.
Ozone has been used in the treatment of drinking water for over eighty years and has gained widespread use in the water treatment industry largely from the fact that it is the second most powerful oxidant known. This fact results in three distinct uses of ozone: the control of pollutants, as a sterilant for microorganisms, and in deodorization. Ozone has also been used in the laundry industry.
Ozone acts as a positively charged molecule that is electron deficient. Organic and hydrocarbon stains such as greases, fats, and oils have centers of high electron density and carry a negative charge. When ozone is injected into a washing machine, it is attracted to these molecules. It then reacts chemically with the soil in an oxidation process. The kinetics of the reaction between soil and ozone is very high; thus, the reaction between these two substances is extremely fast. The ozone will begin to react within a fraction of a second after contact. In the process the ozone will give up its third oxygen atom which will chemically bond with the soil molecule. An oxygen atom is highly electronegative and when added to a soil molecule, the electronegative charge will cause the chemical double bond of the molecule to polarize (reverse charge). Polarization will cause a large soil molecule to fragment into several smaller molecules. The strength of attachment between soil and a textile is largely a function of the size of the soil molecule. Smaller soil molecules will be more easily removed from the textile. The size of the molecule also has a direct effect on the solubility of the soil whereby a reduction in size will greatly increase the amount of soil that is dissolved in the wash liquor.
Surfactants and alkalis are used in most laundry detergents. Their main purpose is to suspend soil by bonding with the soil molecules to prevent redeposition of the soil. However, surfactants also play a key role in loosening of the soil. Some soils can be removed from the textile surface by mechanical action and water alone, but the majority cannot. Thus, a major part of the role of the surfactant is to loosen soil from the textile. However, this task can also be accomplished by ozone. A primary purpose of ozone in laundry processing is to remove the soil from the textile through polarization. A secondary purpose is to oxidize the soil, making it more soluble and allowing for faster precipitation. Ozone is in a highly reactive gaseous form in laundry processing, allowing it to react with and remove soil at a greatly increased rate which accounts for a substantial reduction in processing time. For these reasons, excellent results can be achieved using ozone and only about half the amount of surfactants usually required.
Alkalis are used for controlling the pH and alkalinity of the wash water. They also bond with calcium and magnesium allowing the surfactants to react with soils more effectively. A problem occurs in that when the alkali bonds with the calcium and magnesium, it can no longer contribute to the washing process. However, when ozone comes in contact with the bonded alkali, it will oxidize the ions, causing the calcium and magnesium to form a precipitate. The alkali is then free to react again. Thus, when using ozone as a wash chemical, it is only necessary to use a small amount of alkali on heavy industrial soil and in the bleach cycle for pH control. Otherwise, it is not necessary to use any alkali with high concentration ozone washing.
The use of ozone in the laundry process reduces or eliminates the need for other laundry chemicals and finishing products such as antichlor, "sour", bactericides, and mildewcides. Antichlor is used to neutralize any residual chlorine bleach. Ozone oxidizes chlorine bleach and completely neutralizes it. For this reason, ozone is not used in a chlorine bleach cycle. However, since ozone has bleaching capability, the need for chlorine bleach is reduced and, consequently, the need for antichlor. Sour is used to neutralize the effects of alkali on the pH of the wash solution. Since the use of ozone greatly reduces the need for alkali, the need for sour is also reduced. The high oxidizing power of ozone will destroy bacteria quickly. Ozone is one of the most lethal and efficient killers of bacteria known, as will be detailed further below. Thus, the need for an additional bactericide is eliminated when ozone is used in laundry processing. Mildewcide is used to combat the growth of mildew on textiles. Although ozone is a highly effective agent in killing mildews, the effect of ozone is not persistent. Thus, mildewcide use may be necessary during seasons when mildews proliferate, although in greatly reduced quantities.
Ozone acts about 3000 times faster than chlorine as a bactericide and is the strongest oxidant commercially available for the treatment of water. Ozone has been used in the treatment of drinking water since 1906, when it was first installed in Nice, France. Ozone destroys bacteria, viruses, mold, fungi, and algae more effectively than any other biocide available for two reasons. Ozone has a much higher oxidation potential than chlorine, and its mechanism of kill is unique. Chlorine must first diffuse through the cell wall to kill the microorganism internally. This process can take 30 to 60 minutes. Reactivation of the cell can occur if contact time or concentration are not sufficient. Ozone, on the other hand, kills bacteria in just a few seconds by a process known as cell lysing. It molecularly ruptures the cell membrane and scatters the inner cytoplasm. Thus, ozone destroys the microorganisms and prevents them from developing ozone resistant strains, eliminating the need to periodically change bactericides.
Additional benefits from using ozone in laundry processing are dramatically increased washroom capacity due to decrease in processing or "formula" time, reduction in washroom labor, increased textile life, reduced water usage, and reduced utility consumption. The soil oxide is easier to remove and precipitate which allows for the use of greatly reduced break and suds events and the removal of some of the flushes. By using less chemicals, less rinsing is required to remove the chemicals. The reduction in the number of formula events results in a substantial decrease in water usage and a subsequent decrease in the gallonage discharged to sewers and a decrease in the concentration of COD, FOG, and TSS.